Initialize Nix overlay repository with blueprint, goose-cli, and docs

Add the complete overlay structure using numtide/blueprint with:
- Two overlay strategies (default and shared-nixpkgs)
- goose-cli package with custom librusty_v8 fetcher
- Interactive package launcher via fzf
- Flake input caching utility
- Comprehensive README and AGENTS.md documentation

packages/flake-inputs/default.nix

@@ -0,0 +1,12 @@
+{
+  inputs,
+  pkgs,
+  ...
+}:
+# A derivation that references all flake inputs to ensure they get cached
+pkgs.runCommand "flake-inputs" { } ''
+  echo ${pkgs.lib.concatMapStringsSep " " (name: inputs.${name}) (builtins.attrNames inputs)} > $out
+''
+// {
+  passthru.hideFromDocs = true;
+}